Photolithographic process



`une 16, 1936. w. H. HACKETT ET AL PHoToLITHocTRAPHIo PRocEss Filed Aug. 29, 1953 Patented June 16, 1936 Ni'rs sTArss 'l` QFFICE PHOTOLITHOGRAPHIC PROCESS Australia Application August 29,

1933, Serial No. 687,366

InV Australia August30, 1932 1 Claim.

This-invention relates to improvements in and connected with photo-lithographic processes which function to reproduce an artist's picture whichis in colours by printing the said picture in like colours.

Although the'invention is essentially simple its application results in an important saving of time and labour of the skilled and experienced artist whose work generally' includes the preparation of a key drawing or outline of the colour components of the picture and whose work also includes the matter of determining the requisite number of different black and white representations each of adiiferent colour component (that is to say the requisite number of printing surfaces) to ensure correct reproduction of the original picture in colours by successive printing operations in diiferent colours.

Reduction of the number of such printing "'plates (and therefore of printings) as against the number employed by known multi-colour printing processes while yet securing the same variety of tones and tone values in the finished printed production, is an objective of the present invention.

The present invention does not depend for its effect upon nor does it include any photographing of the copy through a cross-lined screen which latter process forms the fundamental principle of the well known half-tone process, although the present invention does depend to an extent for its ultimate effect upon printings from metallic printing surfaces comprised by aggregations of dots or marks which metallic printing surfaces are as will be seen produced under the control'of the hand of the artist and are therefore of character capable of being readily differentiated from half-tone printing surfaces prepared solely by photographic and mechanical means. or processes.

The present invention contemplates the preparation in an enlarged size of the representation of each different colour component by markings applied by the artist's hand upon the grained surface area of a plate of zinc, and its subscquent reproduction photographically in size reduced from such enlargement upon another smaller zinc plate having a grained surface. A maximum of tone Value eect is found to be secured to the finished printed production produced by the use of printing plates formed from the last mentioned photographic reductions.

It is here acknowledged that the use of enlargements worked up by hand for subsequent reproduction on a reduced scale is known, and

that the use of a grained surface upon which' any partv of a pictureoor design can be be produced by hand (that is, by the artistis techniquel is well known.

The'invention, briefly stated, comprises a process which following upon the preparationfrom an original coloured picture'of a usual key or outline drawing'indicating the'colour components of' the original includes thev steps of (a) preparing from the key drawing a number of separate enlargements of the sameasv upon the grained surfaces of zinc or like metal plates which in number correspond with the number of colour printings to beV superimposed in the finished-printed production; thefirst one of said key drawing enlargements being preferably photographically prepared and subsequent copies of the same beingV preferably'producedv by a known dust impression transfer method (b) painting in the said'enlargements with black crayon or lithographic ink in a manner so that each'separate enlargement may constitute arepresentationof a diiferent one of thecolour components of the complete picture and (c) 1preparing from the 'last-mentioned'representations `protographicreproductions in reducedv size upon smaller surfaces of other grained zinc or like metal plates in like number anddesigned to be formed by known means into printing surfaces from which-may be secured by successive printings upon the same paper or like smoothv surface the finished? coloured picture or print; such varioussteps co'mprising the complete process according to the invention being utilized in combination for convenient? application for the production vofv photo-mechanical printing surfaces for multi-colour printing.

One application of the invention will be found to be' clearly exemplifiedl by the accompanyingv drawing'-l (which inblackand white) functions to represent? the result's'of varioussteps in the process as hereinbefore mentioned, for the reproduction by printing and by the use of the three primary colours only, of the coloured representation of an apple in small dimension. Neither the original picture or the finished print of the coloured representation of an apple which is indicated as processed according to the invention is indicated by the drawing wherein:

Figure 1 showsthe original key or outline drawing indicating approximately in outline the various colour components of the original picture.

Figure 2 shows one of three identical enlargements of the key or Outline drawing indicated by Figure 1.

Figure 3 shows one of the said three enlarge- 55 ments painted in so that it becomes a separate representation of the blue colour component of the complete picture, it being deemed to be unnecessary for purposes herein to also illustrate the corresponding separate enlargements of the yellow and red colour components of the same picture.

Figures 4, 5 and 6 show reduced reproductions from the said three enlargements of the blue, yellow, and red colour components respectively;

Figure 7 is a very much enlarged view, (magnified say twenty times) of a small portion of or area .of a finished printing surface such as those indicated by Figures 4, 5 and 6 and serves to illustrate by way of example only the general nature of aggregations of dots or marks which directly represent the artist's technique as he originally applied it by markings by varying pressure of his hand upon the chalk or the like to and upon the grained surface of a zinc plate indicated by Figure 3.

A key-drawing being first prepared, upon lithographic paper celluloid or the like photographic enlargements are then prepared in any known manner, as for example by projection of the key drawing from a lantern slide by an intense lantern light on to the grained surfaces of the larger zinc or like metal plates whose surfaces have been first sensitized by being prepared in known manner to receive photographic impressions.

If desired, copies of one said photographic enlargement may be reproduced in other approved manner known in the art, as for example by dusting the photographic enlargement and securing a pull on paper of an outline of it which dust impression is transferre'd to the separate grained zinc or like metal surfaces.

Each said key drawing enlargement is now painted in by black crayon or lithographic ink according to the particular colour component it is ultimately to represent by one printing operation, and the markings are applied in densities or intensities according to the artist's conception as to what is required and as to how such will appear when subsequently photographically reduced in size and so reproduced as upon the printing faces of printing plates or thelike.

Each painted in key drawing enlargement is now photographically reproduced in reduced size by securing from it a photographic negative of requisite reduced size and by printing from the latter directly upon another smaller grained zinc or like metal surface which has been suitably sensitized, and each said photographic reproduc- `,tion in reduced size obviously shows reduced in like proportion on the one hand the representation of the drawing as a whole and on the other hand each separate dot or mark constituting a part of the whole, the effect of the said reduced reproduction so far as tone value is concerned when Viewed by the human eye being infinitely finer than is the tone value effect upon the human eye when viewing from the same distance the drawing from which was made the said reduced reproduction.

In other words, because of the relative coarseness of the said dots or marks, should printings be arranged from reproductions of the same which have not been first reduced in size, there would be rendered necessary a much greater number of plates and of printings to secure the requisite finished printed coloured show card or like production which withal would fail to show that depth of tone value arrived at by the present invention.

It will be seen that the present invention provides for the use of the camera preferably in two steps in the process, to first enlarge and then reduce upon grained metal surfaces, and that the camera is definitely used for the reduction step from one grained metal surface to another, and all in such manner that whereas in some cases according to other known processes as many as ten or more plates and printings may be necessary, three such have in the process according to the invention been found to secure a finely finished and perfectly printed coloured picture ofl the same character.

From the smaller grained metal plates which steps of, photographically preparing from the key' drawing a number of separate enlargements of the same upon the grained surfaces of metal plates which in number correspond with the number of 'colour printings to be superimposed in the finished printed production, painting in the said enlargements in manner so that each separate one of them may constitute a representation of a different one of the colour components of the complete picture and, preparing from the lastmentioned representations photographic reproductions in reduced size and upon smaller surfaces of other grained metal plates in like number designed to be formed by known means into printing surfaces in manner so that successive printings from them upon the same smooth paper surface may form the finished coloured picture, or print.

WILLIAM HENRY HACKETT. PERCY WILLIAM PRYKE. 

